Properties of Fe-bearing Mg silicate glasses as novel supplementary cementitious materials

• Fe-Mg silicate glasses show potential as supplementary cementitious materials. • Glass materials show pozzolanic activity similar or higher than slag/fly ash. • Glass mortars reach up to 20 % higher 28-day strength than control sample. • Glasses boost early hydration heat and shift paste hydration kinetics. • Mortars show enhanced C-(A-)S-H and Mg-Al(Fe) LDH formation than control sample. Blended cements incorporating supplementary cementitious materials (SCMs) offer a viable strategy for reducing the carbon footprint of Portland cement. As traditional SCMs (e.g., blast furnace slags, coal fly ash) become increasingly scarce, the development of alternative materials is crucial. This study evaluates synthetic Fe-bearing Mg silicate glasses as potential low-carbon SCMs, free from direct CO 2 emissions associated with raw material processing. Three types of synthetic glasses (Mg-Si, Fe 3+ -Mg-Si, and Fe 2+ /Fe 3+ -Mg-Si glasses) were assessed for their pozzolanic activity and used to replace 20 wt% of Portland cement. Mortar samples incorporating these glasses demonstrated a strength activity index increase of up to 120 % compared to the control. Microstructural analysis revealed enhanced formation of C-(A-)S-H and Fe-bearing Mg-containing phases, including Mg-Al(Fe) layered double hydroxides (LDHs). The incorporation of Fe was observed to promote Al mobilization, facilitating early sulfate reactions and potentially influencing cement hydration kinetics. This work shows how non-conventional glass-based SCMs can be engineered to enhance blended cement performance while lowering carbon emissions.